Monkeys are a group of primates found in both the "New" and the "Old" World. The term "monkey" is actually a laypersons term for any one of the generally small-bodied and often distantly related primates that do not fall into the classification of prosimians or the generally larger bodied apes and humans. There are two basic types of monkeys - platyrrhines and catarrhines.[1][2] South American monkeys are known as platyrrhines and differ substantially from the catarrhines monkeys, having evolved largely in isolation.[1][2]
The name platyrrhine is derived as a descriptive term of the monkeys' faces, since South American monkeys have broad, flat noses. All platyrrhine monkeys are small - the largest is only around 10kg.[1] They also exhibit many primitive dental and skeletal features including having three pre-molars in each side of their mandible and maxilla - thus they have a total of twelve premolars.[2]
All platyrrhines have a tail of some sort and five genera have prehensile tails.[1] The most well known of the prehensile-tailed monkeys is probably the spider monkey. Interestingly, the spider monkey has no thumb.[1]
Catarrhines monkeys are "Old World Monkeys" and all fall under the Superfamily Cercopithecidae.[2] They have narrow noses, eight pre-molars and none have prehensile tails.[1] There are two Subfamilies within the Superfamily - Cercopithecinae and Colobinae.[2] There are approximately sixty species of cercopithicus monkey and about forty species of colobus monkey.